[0001] This invention relates to refrigeration cycles using a mixed refrigerant.
[0002] In a refrigeration cycle, low pressure vapour is compressed and the compressed vapour
is thereafter cooled and condensed and the high pressure condensed stream expanded
back to the low pressure to form a returning low pressure refrigerant stream which
is vaporised to re-form the low pressure vapour stream for return to the compressor.
The final cooling and condensation of the compressed vapour is effected in indirect
counter-current heat exchange with the vaporising low pressure stream. Cooling of
the material to be refrigerated is by heat exchange with the vaporising low pressure
stream.
[0003] In a refrigeration cycle utilizing a multi-component refrigerant, sometimes known
as a mixed refrigerant refrigeration cycle, the refrigerant stream is made up of a
plurality of components having differing boiling points. The compressed vapour thus
condenses over a range of temperatures and likewise the condensed refrigerant boils
over a range of temperatures. Such a refrigeration cycle is known from US-A-5,613,373.
[0004] These mixed refrigerant refrigeration cycles are used extensively, especially but
not exclusively for natural gas. Because of the wide use of these systems, improvements
in efficiency are always being sought, both in the sense of economy of operation and
in simplification of the plant. Because of the scale of the plants, especially for
the liquefaction of natural gas, even small improvements can substantially affect
the viability of a plant.
[0005] This invention provides an improvement to the mixed refrigerant refrigeration cycles
[0006] According to the present invention there is provided a refrigeration cycle utilizing
a multi-component refrigerant wherein the compression of low pressure refrigerant
vapour is effected in at least two stages of compression with cooling, partial condensation
and separation from the uncondensed vapour of the entire condensate formed after each
of at least two of the said stages thereby providing two or more condensate streams
of different compositions and at different pressures and wherein at least two of said
condensate streams are expanded and injected into the returning low pressure refrigerant
at different temperatures of said low pressure refrigerant.
[0007] In one preferred embodiment, at least one of the said condensate streams is sub-cooled
prior to the said expansion. In one aspect of this embodiment, at least two of said
streams are sub-cooled to the same temperature; alternatively, however, they may be
sub-cooled to different temperatures. It is to be understood, however, that even if
sub-cooled to the same temperature at least two of the said condensate streams must
be injected into the returning low pressure refrigerant at different temperatures.
[0008] In one embodiment of the invention, vapour recovered from the last stage of compression
is subjected to two or more steps of cooling and partial condensation with separation
of condensate from uncondensed vapour after each step and each separated condensate
is thereafter expanded and injected into returning low pressure refrigerant. Preferably,
at least one of the separated condensates is sub-cooled. One or more of these cooling
steps may be effected by indirect countercurrent heat exchange with returning low
pressure refrigerant.
[0009] Further improvements may be achieved if a refluxing exchanger is employed in the
generation and separation of condensate from uncondensed vapour in one or more of
the vapour/liquid separation steps in the cycle. The use of a refluxing exchanger
in the generation and separation of condensate from uncondensed vapour in a refrigeration
cycle utilizing a multi-component refrigerant and including at least one step of cooling
and partially condensing compressed vapour and separating the condensate so formed
from uncondensed vapour is the subject of GB patent application 9712301.2 filed on
12 June 1997.
[0010] The invention will now be described in greater detail with reference to preferred
embodiments thereof and with the aid of the accompanying drawings in which
Figure 1 is a flow sheet of a known mixed refrigerant refrigeration cycle for use
in the liquefaction of natural gas;
Figure 2 is a flow sheet of another known mixed refrigerant refrigeration cycle;
Figure 3 is a flow sheet of a refrigeration cycle in accordance with the present invention;
Figure 4 is a flow sheet of a modification of the refrigeration cycle of Figure 3
wherein two stages of aftercooling are provided;
Figure 5 is a flow sheet of another modification of the refrigerant cycle of Figure
3 wherein a refluxing exchanger is employed to generate and separate a condensate
stream; and
Figure 6 is a flow sheet of a modification of the refrigeration cycle of Figure 5
in which condensate formed in the compressed vapour during cooling by indirect countercurrent
heat exchange with returning low pressure refrigerant is separated from the uncondensed
vapour at an intermediate point of the heat exchanger.
[0011] In the following description, the invention will be described with reference to the
liquefaction of natural gas; however, it is to be understood that the use of the refrigeration
cycles of this invention is not so limited and that they are also suitable for use
in other applications, eg. for other gas liquefaction processes or for purification
by partial condensation techniques.
[0012] Referring now to Figure 1 of the drawings, which provides a flow sheet of a known
mixed refrigerant refrigeration cycle for the liquefaction of natural gas, the natural
gas which is to be liquefied, is supplied at an elevated pressure to a heat exchanger
4 through line 2 and the liquefied product is recovered through line 6. The details
of the arrangement for recovering the liquefied product are not relevant to the invention
and many variants are possible but in the embodiment illustrated the gas is first
cooled and partially condensed to recover a heavy hydrocarbon fraction.
[0013] The condensate is separated from uncondensed gas in liquid/vapour separator 8. Condensate
is recovered in line 10 and the uncondensed gas is returned to a cooler section of
the heat exchanger in line 12 for a further step of cooling and partial condensation
with the further condensate being separated from the uncondensed gas in liquid/vapour
separator 14. The uncondensed gas is again returned to the heat exchanger, this time
to the cold end, in line 16 for final cooling and condensation after which it is recovered,
expanded to an intermediate pressure through valve 18 and supplied to liquid/vapour
separator 20 for separation of any uncondensed gas. Condensate recovered from the
separator 20 in line 22 is further expanded to its final pressure in expansion valve
24 and supplied to liquid/vapour separator 26 from which the liquefied gas is recovered
in line 6 as mentioned above. Uncondensed gas from separator 20 is returned via line
30 to be reheated in heat exchanger 4 and is then combined with condensed liquid in
line 32 from separator 14 which has been expanded through valve 34. The combined stream
is further warmed in heat exchanger 4 and then recovered therefrom in line 36. It
is thereafter joined by the cold uncondensed gas from separator 26 in line 38.
[0014] The cooling and liquefaction of the natural gas is effected in heat exchanger 4 by
indirect countercurrent heat exchange with a vaporising mixed refrigerant stream in
line 40. For the liquefaction of natural gas, the mixed refrigerant preferably comprises
a mixture of nitrogen and C
1 to C
5 hydrocarbons.
[0015] The low pressure vaporised stream recovered from the heat exchanger in line 40 is
recycled for recompression in a two stage compressor having first and second stages
42, 44. After compression in the first stage 42, the vapour is transferred via line
46 for cooling in inter-cooler 48 and then passed via line 50 to vapour/liquid separator
52 for the separation of condensate formed by the cooling in the inter-cooler. The
uncondensed vapour is recovered in line 54 and transferred to the second stage 44
of the compressor, the compressed vapour therefrom being collected in line 56 for
transfer to after cooler 58 where it is cooled and partially condensed. The partially
condensed high pressure stream is recovered in line 60. Condensate formed as a result
of cooling in the inter-cooler 48 is recovered from vapour/liquid separator 52 in
line 64, pumped up to the same pressure as the stream in line 60 by pump 66, and combined
with that stream for supply to the vapour/liquid separator 62.
[0016] Uncondensed vapour from vapour/liquid separator 62 is recovered overhead in line
68. Condensate recovered in line 70 is pumped by pump 72 to rejoin the overhead vapour
via line 74. The combined stream is then passed through heat exchanger 4 in line 76
where the vapour is cooled and condensed in indirect countercurrent heat exchange
with the vaporising refrigerant stream in line 40 and thereafter expanded through
valve 78 into the low pressure line 40 to form the returning low pressure refrigerant
stream.
[0017] A known modification of the refrigeration cycle shown in Figure 1 will now be described
and illustrated with reference to Figure 2, wherein pipelines and apparatus components
common to the embodiment illustrated in Figure 1 are accorded the same reference numerals.
In this modification, the condensate recovered from vapour/liquid separator 62 is
not injected back into the overhead vapour in line 68 but is recovered in line 90
and directed into the warm end of heat exchanger 4 where it is sub-cooled in indirect
countercurrent heat exchange with the vaporising returning low pressure refrigerant
in line 40. It is then recovered from heat exchanger 4 at an intermediate point thereof,
expanded to about the pressure of that low pressure stream and injected into that
stream through line 94.
[0018] An arrangement according to the present invention will now be described with reference
to Figure 3 which illustrates the application of the invention to the prior art process
illustrated in Figure 2 and in which all lines and apparatus components common with
those of Figure 2 are accorded the same reference numerals. In the refrigeration cycle
illustrated in Figure 3, the modification of the arrangement of Figure 2 lies in the
treatment of the condensate formed in inter-cooler 48. In accordance with the invention,
condensate formed in inter-cooler 48 and separated from uncondensed vapour in vapour/liquid
separator 52 is recovered in line 102, in which it is directed into heat exchanger
4 at the warm end thereof and wherein it is sub-cooled by indirect countercurrent
heat exchange with vaporising returning low pressure refrigerant in line 40, expanded
to substantially the same pressure as said returning low pressure refrigerant in valve
104 and injected through line 106 into said low pressure refrigerant in line 40 at
a higher temperature than that at which the condensate in line 94 is injected. It
will be understood that the condensate in line 102, which was formed in the inter-cooler
will be at a lower pressure than that in line 90 which was formed in the aftercooler.
The condensate in line 102 is injected into the returning vaporising low pressure
refrigerant stream at a higher temperature than that at which the condensate in line
90 is injected because the condensate in line 102 will have a higher boiling range
than that in line 90.
[0019] As will be seen with reference to Figure 3, in the refrigeration cycle according
to the invention, the heavier liquid condensed in the compressor interstage cooler
48 is used as a separate refrigerant stream from the liquid condensed in the aftercooler
58. The interstage liquid is subcooled separately and is injected into the returning
stream 40 at a higher temperature level than the liquid from the aftercooler. This
in effect creates a complete-additional refrigerant stage. This results in lower power
consumption and/or a reduction in heat exchanger size due to the following:
a) the interstage liquid is no longer pumped to discharge pressure;
b) the heavier components condensed in the interstage are injected into the vaporising
return low pressure refrigerant at a temperature level where they can be most beneficial,
thus improving the match between the low pressure refrigerant H/T curve and the combined
cooling curve of the high pressure streams. This results in an improvement in thermodynamic
efficiency;
c) less heavy components are contained in the liquid leaving the separator after the
aftercooler. Thus less total refrigerant fluid is processed by the heat exchanger
below the point of injection of the interstage liquid. Also, the return refrigerant
below this point is lighter and therefore evaporates more easily, thus improving the
heat transfer efficiency and reducing the heat exchanger duty;
d) the degree of sub-cooling of the separate liquid streams can be more easily optimised
to minimise the amount of flash on expansion to the common low pressure, and therefore
reduce the complexity and cost of equipment required to achieve good two-phase distribution.
[0020] A further benefit of the refrigeration cycle according to the invention is that it
permits greater operational flexibility to cope with variation in gas composition,
temperature and/or pressure and in changes in ambient conditions.
[0021] While in the embodiment of Figure 3 there are two stages of compression and two condensate
steams are obtained, the invention is also applicable to three or more stages of compression
in which case any two or more of the condensate streams so obtained may be expanded
and injected into the returning low pressure refrigerant. Preferably, at least one
is sub-cooled to an appropriate temperature before expansion.
[0022] If desired, two or more steps of cooling and separation of condensate may be effected
after each stage of compression. It will be understood that the resultant condensate
streams will be at substantially the same pressure although of different composition.
[0023] An application of the invention to such an arrangement is illustrated in Figure 4
which is a modification of the arrangement of Figure 3 wherein two stages of after
cooling are provided. In this Figure, wherein the same pipelines and apparatus components
as those of Figure 3 are accorded the same reference numerals, the compressed refrigerant
stream recovered from final compressor stage 44 in line 56 is cooled and partially
condensed in first after-cooler 58A and the partially condensed stream is conveyed
via line 60A to a first vapour/liquid separator 62A condensate from which is recovered
in line 90A, subcooled in heat exchanger 4 in indirect countercurrent heat exchange
with returning vaporising low pressure refrigerant in line 40, expanded in expansion
valve 92A to substantially the pressure of said low pressure refrigerant and injected
into it through line 94A. The uncondensed vapour from liquid/vapour separator 62A
is further cooled and partially condensed in second after cooler 58B and the condensate
formed therein is separated from uncondensed vapour in liquid/vapour separator 62B.
recovered in line 90B and likewise sub-cooled, expanded (through expansion valve 92B)
and injected (via line 94B) into the returning low pressure refrigerant stream. It
will be understood that the condensate streams in lines 90A and 90B will be of different
composition but at substantially the same pressure which will be a higher pressure
than that of the condensate in line 102 which has been formed in inter-cooler 48.
[0024] Still further improvement is achievable if a refluxing exchanger is employed in the
generation and separation of a condensate. An application of this embodiment of the
invention is illustrated in Figure 5 which is a modification of the arrangement of
Figure 3 and where all pipelines and apparatus components common with Figure 3 are
accorded the same reference numerals. In the arrangement of Figure 5, the after cooler
58 and liquid/vapour separator 62 of the arrangement of Figure 2 are replaced by a
reflux exchanger 120. The compressed refrigerant recovered from the final stage 44
of compression is directed via line 56 to reflux exchanger 120 where it is cooled
and partially condensed while being directed upwardly through the exchanger. Uncondensed
vapour is recovered from the top of the exchanger through line 68 while condensate
formed in the exchanger travels back down through the exchanger in direct countercurrent
contact with the rising vapour and is collected from the bottom of the exchanger in
line 90. As a result of replacing the after-cooler 58 and liquid/vapour separator
62 by the refluxing exchanger 120, the concentration of light components in the condensate
in line 90 can be minimised thus enabling the condensate to be subcooled to a temperature
where little or no flash occurs on expansion into the returning low pressure refrigerant.
This greatly reduces the complexity and cost of equipment necessary for achieving
good two-phase distribution. There is also a concomitant reduction in the heavy hydrocarbon
content of the vapour leaving the reflux condenser, thus reducing the circulating
flow and improving the thermodynamic efficiency in the lower temperature sections
of the refrigerant circuit.
[0025] A refrigeration cycle utilizing a multi-component refrigerant and including at least
one step of cooling and partially condensing compressed vapour and separating the
condensate so formed from uncondensed vapour to form a condensate stream which is
thereafter expanded and injected into returning low pressure refrigerant, wherein
a refluxing exchanger is employed in at least one of said steps of cooling and partially
condensing to effect at least a part of the cooling and to separate condensate from
uncondensed vapour, is the subject of GB Patent application 9712301.2 filed on 12
June 1997 (GB-A-2326464).
[0026] While the invention has so far been described with reference to the treatment of
condensates formed in the compressor inter cooler and after cooler stages, it will
be understood that as the refrigerant comprises a mixture of components having different
boiling points, condensate may also be recovered at one or more points in the course
of the cooling of the compressed refrigerant by indirect countercurrent heat exchange
with the low pressure refrigerant in heat exchanger 4.
[0027] This embodiment is illustrated in Figure 6 which is a modification of the arrangement
of Figure 5 and wherein pipelines and apparatus components common with Figure 5 are
accorded the same reference numerals. In the arrangement of Figure 6 the compressed
refrigerant vapour recovered overhead from the refluxing exchanger 120 in line 68
and passed through heat exchanger 4 in line 76 is withdrawn from heat exchanger 4
at an intermediate point where it is not fully condensed. The condensate is separated
from uncondensed vapour in liquid/vapour separator 202, subcooled in line 204 in indirect
countercurrent heat exchange with vaporising returning low pressure refrigerant, expanded
through expansion valve 206 to about the same pressure as said low pressure refrigerant
and thereafter injected into it.
[0028] By this means, condensate formed in the compressed refrigerant may be recovered from
it close to its dewpoint and then re-injected into returning low pressure refrigerant
stream close to its boiling point, thereby further improving heat transfer efficiency
and reducing the heat exchanger duty.
[0029] Whilst this modification has been described with reference to the arrangement of
Figure 5 wherein a refluxing exchanger is employed to generate and recover condensate
from the compressed stream recovered from the last stage of the compressor, it will
be understood that it is also applicable to the refrigeration cycles illustrated in
Figures 3 and 4.
[0030] It is further to be understood that while the condensate in line 204 of Figure 6
is shown as being sub-cooled prior to expansion, it need not be sub-cooled although
the benefit obtained is then reduced.
[0031] While the separation of only one such condensate and its treatment is shown, more
than one may be thus separated and treated if desired, by repeatedly separating condensate
from the condensing compressed refrigerant stream as it travels from the warm end
to the cold end of heat exchanger 4 in line 76 (Figure 2), expanding each condensate
so obtained and injecting it into the returning low pressure refrigerant. Each such
condensate may or may not be sub-cooled prior to expansion, as desired.
[0032] While in Figures 5 and 6, a refluxing condenser is shown as replacing the compressor
after cooler and associated vapour/liquid separator, it will be understood that it
may also be employed, additionally or alternatively, to replace a compressor inter-cooler
such as inter-cooler 48 and associated vapour/liquid separator, such as separator
50, and possibly also even in the generation and separation of other condensate streams
in the refrigeration cycle by partial condensation of compressed refrigerant. Each
refluxing exchanger may also be used to provide less than all the cooling and thus
used in series with a conventional inter-cooler or after cooler as well as a total
replacement therefor.
[0033] One or more of the expansion valves employed for the expansion of condensate in any
part of the refrigeration cycle may, if desired, be replaced by devices in which expansion
is effected with performance of external work, e.g. a turbine expander.
[0034] It will be understood that while heat exchanger 4 is shown as being a single heat
exchanger, its overall function may be supplied by a plurality of exchangers.
[0035] It will generally be preferred for at least any heat exchanger employed in the indirect
counter-current heat exchange of compressed refrigerant with returning low pressure
refrigerant to be a multi-stream plate fin type heat exchanger because such heat exchangers
provide greater flexibility to efficiently process a multiplicity of different streams.
[0036] While the invention has been described with particular reference to the liquefaction
of natural gas, it may also be used in other cryogenic applications e.g. for the liquefaction
of streams or for purification where one or more contaminants is or are removed by
cooling and partial condensation. Examples include air separation, the treatment of
refinery off
gas, and the liquefaction of ethylene and ethane.
[0037] Any suitable combination of two or more refrigerants may be used in the mixed refrigerant
cycle and the choice will depend upon the composition of the material to be refrigerated
and the temperature to which it is to be cooled. Examples of suitable refrigerants
include nitrogen, low boiling halogenated hydrocarbons, eg. chlorofluorocarbons, and
low boiling hydrocarbons. In general however, the mixed refrigerant will usually comprise
two or more of nitrogen and C
1-C
5 hydrocarbons.
[0038] If desired, one or more of the condensate streams formed in the refrigeration cycle
of the invention may be divided into at least two sub-streams having the same composition
and the said sub-streams may each be expanded and injected into the returning low
pressure refrigerant stream at different temperatures of the returning low pressure
refrigerant. This enables the evaporation characteristics of the low pressure refrigerant
to be changed progressively to better match the combined cooling curve of the high
pressure streams, thereby still further improving the efficiency of the refrigeration
cycle. A refrigeration cycle utilizing a multi-component refrigerant and including
at least one step of partially condensing compressed vapour, forming a condensate
stream by separating condensate so formed from uncondensed vapour and thereafter expanding
said condensate stream and injecting said expanded condensate stream into returning
low pressure refrigerant, characterised in that said expanded condensate stream is
injected into said returning low pressure refrigerant in the form of at least two
sub-streams formed by division of said condensate, at least two of said sub-streams
being injected into the returning low pressure refrigerant at different temperatures
of the returning low pressure refrigerant is the subject of GB patent application
9712302.0 filed on 12 June 1997 (GB-A-2 326465).
EXAMPLE
[0039] The invention is now illustrated by the following Example.
[0040] First, in a comparative experiment, a multi-component refrigerant stream of the composition
shown (as mol. %) in Table 1
Table 1
NITROGEN |
6.33 |
METHANE |
22.27 |
ETHANE |
43.98 |
PROPANE |
6.00 |
i-BUTANE |
3.39 |
n-BUTANE |
3.39 |
i-PENTANE |
7.32 |
n-PENTANE |
7.32 |
is incorporated into the prior art mixed refrigerant refrigeration cycle shown in
Figure 2 at 40. The vapour fractions, temperatures, pressures, flow rates and compositions
of the various refrigerant streams are recorded in Table 2 below. This is used to
cool a natural gas feed and streams produced therefrom. The vapour fractions, temperatures,
pressures, flow rates and compositions of the various streams on the natural gas side
are recorded in Table 3 below.
[0041] In a second experiment, the same multi-component refrigerant stream is incorporated
into the mixed refrigerant refrigeration cycle of the present invention shown in Figure
3 at 40 and this is used to cool the same natural gas feed. The vapour fractions,
temperatures, pressures, flow rates and compositions of the various streams on the
natural gas side are as shown in Table 3 while those for the various refrigerant streams
are shown in Table 4.
[0042] The use of the mixed refrigerant refrigerator cycle of the present invention is found
to give improved efficiency. Thus, the total power consumed in the first experiment
is 53784 KW while that second according to the invention is only 52860 KW, a saving
of nearly 1MW (1.7%). This results in a lower capital and operating cost for the refrigeraton
system. The total UA
1 was also measured in both cases. In the comparative experiment, the value was 34.99
MW/°C while in the experiment in accordance with the invention the value was 34.92
MW/°C. This value is a measure of heat exchanger surface area and shows that the experiment
in accordance with the invention gives a similar surface area for a reduced power
consumption. This results in a similar capital cost for this item of plant. The reduced
capital cost for the refrigerant compression thus gives a net cost benefit.
![](https://data.epo.org/publication-server/image?imagePath=2002/38/DOC/EPNWB1/EP98928467NWB1/imgb0003)
This term is derived form the equation Q=UAaT where Q is the energy transferred; U
is heat transfer coefficient; A is the heat exchange area and ΔT is the temperature
differential.
1. A refrigeration cycle utilizing a multi-component refrigerant wherein the compression
of low pressure refrigerant vapour is effected in at least two stages of compression
(48,58) with cooling, partial condensation and separation from the uncondensed vapour
of the entire condensate formed after each of at least two of the said stages thereby
providing two or more condensate streams (90,102) of different compositions and at
different pressures and wherein at least two of said condensate streams are expanded
and injected into the returning low pressure refrigerant (40) at different temperatures
of said low pressure refrigerant.
2. A refrigeration cycle as claimed in Claim 1 wherein at least one of said condensate
streams is sub-cooled prior to said expansion.
3. A refrigeration cycle as claimed in Claim 1 wherein at least two of said condensate
streams are sub-cooled to the same temperature prior to said expansion.
4. A refrigeration cycle as claimed in Claim 1 wherein at least two of said condensate
streams are sub-cooled to different temperatures prior to said expansion.
5. A refrigeration cycle as claimed in any one of Claims 1 to 4 in which vapour recovered
from the last stage of compression is subjected to two or more steps of cooling and
partial condensation with separation of condensate from uncondensed vapour after each
step and each separated condensate is thereafter expanded and injected into returning
low pressure refrigerant.
6. A refrigeration cycle as claimed in Claim 5 in which compressor after cooling is effected
in stages with separation of condensate formed in each stage to form two or more condensates
having different compositions at substantially the same pressure and said condensates
are separately sub-cooled, expanded and injected into returning low pressure refrigerant.
7. A refrigeration cycle as claimed in Claim 5 or Claim 6 wherein at least one of said
separated condensates is subcooled prior to said expansion.
8. A refrigeration cycle as claimed in any one of the preceding claims in which a refluxing
exchanger is employed in the generation and separation of condensate from uncondensed
vapour in at least one of the steps of cooling, partial condensation and separation
of condensate from uncondensed vapour.
9. A refrigeration cycle as claimed in Claim 8 in which a refluxing exchanger is employed
in the generation and separation of condensate from compressed vapour recovered from
the last stage of compression.
10. A refrigeration cycle as claimed in any one of the preceding claims utilized for the
liquefaction of natural gas.
11. A refrigeration cycle as claimed in any one of the preceding claims wherein the refrigerant
comprises a mixture comprising any combination of two or more of nitrogen and C1 to C5 hydrocarbons.
12. A refrigeration cycle as claimed in any one of the preceding claims wherein one or
more multi-stream plate fin type heat exchangers is or are employed in the cooling
and partial condensation of compressed refrigerant.
1. Kältekreislauf, der ein mehrkomponentiges Kältemittel verwendet, wobei die Kompression
eines Niederdruck-Kältemitteldampfes in mindestens zwei Kompressionsstufen (48, 58)
bewirkt wird, mit Kühlung, Teilkondensation und Abtrennung des gesamten Kondensates,
das sich nach jeder der mindestens zwei der Stufen gebildet hat, von dem unkondensierten
Dampf, wodurch zwei oder mehr Kondensatströme (90, 102) mit unterschiedlichen Zusammensetzungen
und bei unterschiedlichen Drücken bereitgestellt werden, und wobei mindestens zwei
der Kondensatströme expandiert und bei unterschiedlichen Temperaturen des Niederdruck-Kältemittels
in das rücklaufende Niederdruck-Kältemittel (40) injiziert werden.
2. Kältekreislauf nach Anspruch 1, bei dem mindestens einer der Kondensatströme vor der
Expansion unterkühlt wird.
3. Kältekreislauf nach Anspruch 1, bei dem mindestens zwei der Kondensatströme vor der
Expansion auf dieselbe Temperatur unterkühlt werden.
4. Kältekreislauf nach Anspruch 1, bei dem mindestens zwei der Kondensatströme vor der
Expansion auf unterschiedliche Temperaturen unterkühlt werden.
5. Kältekreislauf nach einem der Ansprüche 1 bis 4, bei dem Dampf, der aus der letzten
Kompressionsstufe zurückgewonnen wird, zwei oder mehr Schritten des Kühlens und der
Teilkondensation mit Abtrennung des Kondensats aus dem unkondensierten Dampf nach
jedem Schritt unterzogen wird, und wobei jedes abgetrennte Kondensat danach expandiert
und in zurückkehrendes Niederdruck-Kältemittel injiziert wird.
6. Kältekreislauf nach Anspruch 5, bei dem die Kompression nach dem Kühlen in Stufen
bewirkt wird, mit der Abtrennung von Kondensat, das in jeder Stufe ausgebildet wird,
um zwei oder mehr Kondensate mit unterschiedlichen Zusammensetzungen bei im Wesentlichen
demselben Druck auszubilden, und wobei die Kondensate getrennt unterkühlt, expandiert
und in zurückkehrendes Niederdruck-Kältemittel injiziert werden.
7. Kältekreislauf nach Anspruch 5 oder Anspruch 6, bei dem mindestens eines der getrennten
Kondensate vor der Expansion unterkühlt wird.
8. Kältekreislauf nach einem der vorhergehenden Ansprüche, bei dem ein Rückflusstauscher
bei der Erzeugung und der Abtrennung von Kondensat von dem unkondensierten Dampf verwendet
wird, und zwar in mindestens einem der Schritte des Kühlens, der Teilkondensation
und des Abtrennens von Kondensat von unkondensiertem Dampf.
9. Kältekreislauf nach Anspruch 8, bei dem ein Rückflusstauscher bei der Erzeugung und
Abtrennung von Kondensat aus komprimiertem Dampf verwendet wird, der aus der letzten
Kompressionsstufe zurückgewonnen wird.
10. Kältekreislauf nach einem der vorhergehenden Ansprüche, der für die Verflüssigung
von Erdgas verwendet.
11. Kältekreislauf nach einem der vorhergehenden Ansprüche, bei dem das Kältemittel ein
Gemisch aufweist, das jedwede Kombination aus zwei oder mehreren der folgenden Bestandteile
enthält: Stickstoff und C1- bis C5-Kohlenwasserstoffe.
12. Kältekreislauf nach einem der vorhergehenden Ansprüche, bei dem ein oder mehrere Mehrstrom-Rippenplattenwärmetauscher
beim Kühlen und bei der Teilkondensation des komprimierten Kältemittels verwendet
wird oder werden.
1. Cycle de réfrigération utilisant un réfrigérant multi-composants dans lequel la compression
de la vapeur du réfrigérant à basse pression est effectuée en au moins deux étapes
de compression (48, 58) avec refroidissement, condensation partielle et séparation
entre la vapeur non condensée et la totalité du condensat formé après chacune des
deux dites étapes, créant ainsi au moins deux courants de condensats (90, 102) de
différentes compositions et à différentes pressions, et dans lequel au moins deux
desdits courants de condensats subissent une détente et sont injectés dans le réfrigérant
à basse pression de retour (40) à différentes températures dudit réfrigérant à basse
pression.
2. Cycle de réfrigération selon la revendication 1, dans lequel au moins l'un desdits
courants de condensats est sous-refroidi avant ladite détente.
3. Cycle de réfrigération selon la revendication 1, dans lequel au moins deux desdits
courants de condensats sont sous-refroidis à la même température avant ladite détente.
4. Cycle de réfrigération selon la revendication 1, dans lequel au moins deux desdits
courants de condensats sont sous-refroidis à des températures différentes avant ladite
détente.
5. Cycle de réfrigération selon l'une quelconque des revendications précédentes, dans
lequel la vapeur récupérée à la dernière étape de compression est soumise à au moins
deux étapes de refroidissement et de condensation partielle avec séparation entre
le condensat et la vapeur non condensée après chaque étape, chaque condensat séparé
étant ensuite détendu et injecté dans le réfrigérant de retour à basse pression.
6. Cycle de réfrigération selon la revendication 5, dans lequel la compression après
refroidissement est effectuée par étapes avec séparation du condensat formé à chaque
étape pour former au moins deux condensats avec différentes compositions à essentiellement
la même pression, lesdits condensats étant séparément sous-refroidis, détendus et
injectés dans le réfrigérant de retour à basse pression.
7. Cycle de réfrigération selon la revendication 5 ou 6, dans lequel au moins l'un desdits
condensats séparés est sous-refroidi avant ladite détente.
8. Cycle de réfrigération selon l'une quelconque des revendications précédentes, dans
lequel un échangeur de reflux est utilisé pour la génération et la séparation entre
le condensat et la vapeur non condensée dans au moins l'une des étapes de refroidissement,
de condensation partielle et de séparation entre le condensat et la vapeur non condensée.
9. Cycle de réfrigération selon la revendication 8, dans lequel un échangeur de reflux
est utilisé pour la génération et la séparation entre le condensat et la vapeur comprimée
récupérée à la dernière étape de compression.
10. Cycle de réfrigération selon l'une quelconque des revendications précédentes, utilisé
pour la liquéfaction de gaz naturel.
11. Cycle de réfrigération selon l'une quelconque des revendications précédentes, dans
lequel le réfrigérant comprend un mélange contenant toute combinaison de deux ou plusieurs
hydrocarbures C1 à C5 et d'azote.
12. Cycle de réfrigération selon l'une quelconque des revendications précédentes, dans
lequel un ou plusieurs échangeurs de chaleur multi-courants à plaques sont utilisés
pour le refroidissement et la condensation partielle du réfrigérant comprimé.